The present invention relates to a magnetron sputtering method and apparatus for film formation on a substrate used in the manufacture of semiconductors, optical disks, and electronic components.
FIG. 8 shows a construction of a conventional magnetron sputtering apparatus which is symmetrical about a center axis C. A substrate 5 and a target 100 are arranged opposite each other within a vacuum chamber 10. Gas is introduced from a supply line 11 into the vacuum chamber 10, and discharged from an evacuation line 12. A vacuum gage 13 is provided for monitoring the pressure within the vacuum chamber 10. The target 100 is mounted to the vacuum chamber 10 via an insulator 14. A DC or AC power source 15 is connected to the target 100. Further, a device for monitoring voltage of the target 100 is provided, although not shown. A magnetic circuit 103 is disposed on the backside of the target 100. The apparatus is operated as described below.
An inert gas such as Ar is introduced from the supply line 11 while it is discharged from the evacuation line 12. High voltage is applied to the target 100 by the power source 15 for bringing about electric discharge, whereby Ar is ionized into plasma 117. Ions collide against the negatively biased target 100 and sputter the target 100 to generate sputtered particles. The sputtered particles are deposited on the substrate 5, thereby forming a thin film.
In the magnetron sputtering apparatus, lines of magnetic force 8 are created in a tunnel-like form above the target 100, so that plasma 117 is enclosed within a magnetic field, thereby increasing plasma density and the speed of film deposition. Another advantage of magnetron sputtering is that discharge can be maintained at a low pressure.
In order to satisfy stringent requirements for a substrate for use in the fabrication of semiconductors or the like, it is essential to form a film of extremely high quality. In this regard, the following problems exist in the prior art magnetron sputtering apparatus.
While film formation at a low pressure is desirable for achieving high quality of films formed, a collision rate of electrons and the sputter gas is low at a low pressure making it difficult to produce electric discharge. Accordingly, film formation at a low pressure is usually performed by starting electric discharge as follows.
The pressure within the vacuum chamber 10 is first adjusted to a predetermined pressure P1, at which electric discharge can be started, by controlling the flow rate of Ar or discharge rate thereof from the evacuation line. The predetermined pressure P1 is higher than a target pressure P2. A power source is turned on to apply a high voltage initiating electric discharge. Once electric discharge occurs, large quantities of electrons are generated within the vacuum chamber 10, and because the magnetic field confines the electrons, the electric discharge is maintained even at a low pressure. Therefore, when the start of electric discharge is recognized through monitoring changes in the voltage of the target 100, the pressure within the vacuum chamber 10 is lowered to pressure P2 for achieving film formation to a desired thickness. FIG. 9 is a timing chart showing changes in the pressure and sputtering power in the above described operation.
In the above-described conventional magnetron sputtering method, there is a problem in that the quality of the film which is formed during the time period from t1 to t2 is deteriorated because the target pressure P2 is not reached during this period.
Another problem in the prior art apparatus is that the sputtered particles are deposited on the chamber wall around the substrate. The sputtered particles form a film on the wall, and as the thickness of the film increases, the film eventually falls off and becomes dust. Dust deposited on the substrate deteriorates the quality of the film formed and causes defects in the product. Therefore, it is the normal practice to provide a shield in an area surrounding the substrate and to replace the shield before the sputtered particles deposited thereon start peeling off.
In order to meet demands for higher productivity, however, the electric discharge power needs to be increased, and often the substrate and the target are placed closer to each other. In such cases, the shield is subjected to greater energy of electron collision, and films on the shield are more apt to peel because of thermal shock.
In view of the foregoing, an object of the present invention is to provide a method and apparatus for magnetron sputtering with which high film quality can be achieved.
To accomplish the above object, the present invention provides a magnetron sputtering method, wherein a first target is arranged opposite a substrate while a second target is arranged not opposite the substrate but within the vacuum chamber. Pressure within the vacuum chamber is adjusted to a first pressure, and during a period from the first pressure to a second pressure, which is lower than the first pressure, plasma density above the second target is made greater than plasma density above the first target, and at a time point when the second pressure is reached, the plasma density above the first target is made greater than the plasma density above the second target. According to this method, electric discharge is first brought about above the second target which is not opposite the substrate. Since the second target is not opposite the substrate, sputtered particles are rarely deposited on the substrate during a period from the start of electric discharge until a target pressure, that is, the second pressure, is reached. Also, the electric discharge above the second target supplies electrons which facilitate starting electric discharge above the first target opposite the substrate at a low pressure. Thus, the quality of a film formed at a low pressure can be improved by suppressing film formation at pressures other than the target pressure.
The present invention further provides a magnetron sputtering method comprising the steps of arranging a first target within a vacuum chamber, arranging a substrate opposite the first target within the vacuum chamber, arranging a second target within the vacuum chamber with a face surface not facing the substrate, introducing a gas into the vacuum chamber and adjusting pressure within the vacuum chamber to a first predetermined pressure, providing a first magnet and a second magnet respectively to the first target and the second target for creating magnetic fields above the first target and the second target, movably supporting the first magnet so as to be movable to and from the first target to permit application and removal of the magnetic field above the first target, reducing the pressure in the vacuum chamber from the first predetermined pressure to a second predetermined pressure which is less than the first predetermined pressure, positioning the first magnet away from the first target so that a magnetic field is formed only above the second target by use of the second magnet while the vacuum chamber is at the first predetermined pressure and while the pressure in the vacuum chamber is being reduced to the second predetermined pressure, applying a voltage to the second target to generate plasma at the second target when the pressure is at the first predetermined pressure, and positioning the first magnet near the first target, when the second predetermined pressure is reached, so that a magnetic field is formed above the first target by at least the first magnet and applying a voltage across the first target and the substrate so that film-formation on the substrate is effectuated.
Other and further objects, features and advantages of the invention will appear more fully from the following description.